高温高应变率下钛合金Ti6Al4V的动态力学行为及本构关系

Dynamic Behavior and Constitutive Relationship of Titanium Alloy Ti6Al4V under High Temperature and High Strain Rate

采用分离式霍普金森压杆实验技术,研究了钛合金Ti6Al4V在温度为25~800℃、应变速率为2 000~7 000 s-1的冲击压缩下的动态力学行为和微观组织演变,分析了其力学响应的温度依赖性和应变率敏感性,构建了可准确表征材料塑性流动行为的修正Johnson-Cook模型。结果表明,Ti6Al4V具有显著的应变硬化、应变率强化、应变率增塑和温度软化效应。随着加载温度和应变率的升高,材料的应变硬化效应减弱。温度敏感性随加载温度的升高而显著降低。应变率敏感性因子与加载温度呈负相关,随真实应变的增大呈下降趋势。高温高应变率下细小等轴α相、拉长型α相和块状α相取代初始等轴α相成为Ti6Al4V微观组织的典型特征。考虑率-温耦合作用和绝热温升影响的修正Johnson-Cook模型能够准确地预测Ti6Al4V的塑性流动应力-应变响应。

The dynamic mechanical behavior and microstructure evolution of titanium alloy Ti6Al4V under shock compression at temperatures ranging from 25℃to 800℃and strain rates from 2000 s−1 to 7000 s−1 were studied by using a split Hopkinson pressure bar.The temperature dependence and strain rate sensitivity of the material’s mechanical response were analyzed,and a modified Johnson-Cook model that could accurately characterize the plastic flow behavior of the material was developed.The results show that Ti6Al4V exhibited significant strain hardening,strain rate strengthening,strain rate plasticity,and temperature softening effects.With increasing loading temperature and strain rate,the material’s strain hardening effect is weakened.The temperature sensitivity is significantly decreased with increasing loading temperature.The strain rate sensitivity factor is negatively correlated with the loading temperature,and it shows a downward trend as the true strain increased.At high temperatures and high strain rates,fine equiaxialαphase,elongatedαphase,and massiveαphase replace the initial equiaxialαphase as the typical microstructure features of Ti6Al4V.The modified Johnson-Cook model that considers the effect of rate-temperature coupling and adiabatic temperature rise can accurately predict the plastic flow stress-strain response of Ti6Al4V.